day 14

aoc2023/day14.py

@@ -0,0 +1,122 @@
+import pathlib
+
+base_dir = pathlib.Path(__file__).parent
+filename = base_dir / "day14_input.txt"
+
+Grid = list[list[str]]
+
+
+def load_grid():
+    with open(base_dir / filename) as f:
+        lines: list[str] = f.read().splitlines()
+
+    return [list(line) for line in lines]
+
+
+def print_grid(grid: Grid) -> None:
+    for row in grid:
+        print("".join(row))
+
+
+def roll_rocks(from_row: list[str], to_row: list[str]) -> bool:
+    width = len(from_row)
+    rolled_rock = False
+    for x in range(width):
+        if from_row[x] == "O" and to_row[x] == ".":
+            from_row[x] = "."
+            to_row[x] = "O"
+            rolled_rock = True
+    return rolled_rock
+
+
+def tilt_grid(grid: Grid, direction: str) -> Grid:
+    width = len(grid[0])
+    moved_rock = True
+
+    while moved_rock:
+        moved_rock = False
+
+        if direction == "N":
+            for y in range(1, len(grid)):
+                upper_row = grid[y - 1]
+                lower_row = grid[y]
+                rolled_rock = roll_rocks(from_row=lower_row, to_row=upper_row)
+                if rolled_rock:
+                    moved_rock = True
+        elif direction == "S":
+            for y in range(len(grid) - 1, 0, -1):
+                upper_row = grid[y - 1]
+                lower_row = grid[y]
+                rolled_rock = roll_rocks(from_row=upper_row, to_row=lower_row)
+                if rolled_rock:
+                    moved_rock = True
+        elif direction == "E":
+            for row in grid:
+                for x in range(width - 1, 0, -1):
+                    if row[x - 1] == "O" and row[x] == ".":
+                        row[x] = "O"
+                        row[x - 1] = "."
+                        moved_rock = True
+        elif direction == "W":
+            for row in grid:
+                for x in range(1, width):
+                    if row[x - 1] == "." and row[x] == "O":
+                        row[x] = "."
+                        row[x - 1] = "O"
+                        moved_rock = True
+        else:
+            raise ValueError(f"unknown direction: {direction}")
+
+    return grid
+
+
+def get_grid_load(grid: Grid) -> int:
+    load = 0
+    for y in range(len(grid)):
+        row_multiplier = len(grid) - y
+        n_rocks = sum(ch == "O" for ch in grid[y])
+        load += n_rocks * row_multiplier
+    return load
+
+
+def hash_grid(grid: Grid) -> int:
+    return hash(tuple(tuple(row) for row in grid))
+
+
+def part_1():
+    grid = load_grid()
+    tilt_grid(grid, "N")
+    return get_grid_load(grid)
+
+
+def part_2():
+    grid = load_grid()
+    iterations = 1000000000
+    grid_hashes: list[int] = []
+
+    last_n_unique = 0
+    exit_index = iterations
+    cycle_window = 100
+
+    for i in range(iterations):
+        for direction in "NWSE":
+            tilt_grid(grid, direction)
+
+        grid_hashes.append(hash_grid(grid))
+
+        if i % cycle_window == 0:
+            n_unique = len(set(grid_hashes[-cycle_window:]))
+
+            if n_unique == last_n_unique:
+                exit_index = i + (iterations - i - 1) % n_unique
+
+            last_n_unique = n_unique
+
+        if i == exit_index:
+            break
+
+    return get_grid_load(grid)
+
+
+print(f"answer_p1: {part_1()}")
+print(f"answer_p2: {part_2()}")

aoc2023/day14_test.txt

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+O....#....
+O.OO#....#
+.....##...
+OO.#O....O
+.O.....O#.
+O.#..O.#.#
+..O..#O..O
+.......O..
+#....###..
+#OO..#....